Cement admixture

ABSTRACT

A burned product containing 100 parts by weight of C 2 S, 10 to 100 parts by weight of C 2 AS, and 20 parts by weight or less of C 3 A; a cement admixture prepared by grinding the burned product; and a cement containing 100 parts by weight of ground portland cement clinker and 5 to 100 parts by weight of a ground product of the burned product. Through use of a cement admixture produced by grinding the burned product of the present invention, cement products exhibiting low heat of hydration and good fluidity can be obtained.

TECHNICAL FIELD

The present invention relates to a cement admixture which lowers the heat of hydration of cement, and imparts excellent fluidity to cement.

BACKGROUND ART

Currently, in the cement industry, industrial waste and non-industrial waste are recycled as a raw material for producing cement (see, for example, Japanese Patent Application Laid-Open (kokai) Nos. 56-120552 and 2000-281395). However, when such waste is used in a large amount as a raw material for producing cement, the content of C₃A present in the cement increases, and often leads to the problem that the heat of hydration of the cement increases. Moreover, when mortar or concrete is produced through use of such a cement and an admixture, the slump or mortar flow (i.e., the fluidity of mortar) shrink and cause flow loss and slump loss to increase.

Accordingly, an object of the present invention is to provide a cement admixture which lowers the heat of hydration of cement, and imparts excellent fluidity to cement.

DISCLOSURE OF THE INVENTION

Under the above circumstances, the present inventors have carried out careful studies, and have found that when a burned product of a mixture containing C₂S(2CaO.SiO₂) and C₂AS(2CaO.Al₂O₃.SiO₂) at specified proportions, with C₃A(3CaO.Al₂O₃) content being 20 or less parts by weight, is ground and admixed with portland cement clinker, the resultant cement exhibits low heat of hydration and good fluidity, thereby leading to completion of the present invention.

Accordingly, the present invention provides a sintered product containing 100 parts by weight of C₂S, 10 to 100 parts by weight of C₂AS, and 20 or less parts by weight of C₃A; and a cement admixture prepared by grinding the burned product.

The present invention also provides a cement which contains 100 parts by weight of grinding portland cement clinker and 5 to 100 parts by weight of a ground product of the aforementioned burned product.

BEST MODES FOR CARRYING OUT THE INVENTION

The burned product of the present invention contains C₂S and C₂AS, wherein C₂S accounts for 100 parts by weight and C₂AS accounts for 10 to 100 parts by weight, preferably 20 to 90 parts by weight. When C₂AS content is lower than 10 parts by weight, the amount of free lime (i.e., unreacted CaO) is hard to decrease even with elevated burning temperature during burning, thus hampering successful burning. Moreover, the formed C₂S is highly likely to be γ-C₂S having no hydration activity and thus may greatly deteriorate the strength of the cement. On the other hand, a C₂AS content exceeding 100 parts by weight increases the volume of melt at high temperature, narrowing the burning temperature range. In addition, because C₂S content is low, not only the initial strength but also the long-term strength of the cement deteriorates.

In the burned product of the present invention, the C₃A content with respect to 100 parts by weight of C₂S is 20 or less parts by weight, preferably 10 or less parts by weight. When the C₃A content exceeds 20 parts by weight, heat of hydration of cement increases and fluidity deteriorates.

A burned product satisfying the above compositional requirement may be produced by burning one or more materials selected, for example, from among industrial waste, non-industrial waste, and construction waste soil. Examples of industrial waste include, but are not limited to, coal ash; various types of sludge, such as ready-mixed concrete sludge, sewage sludge, water purifying sludge, construction sludge, and iron-making sludge; and other types of waste such as soil discharged from drilling, ashes from incinerators, molding sand, rock wool, glass waste, secondary ash from blast furnace, construction waste, and concrete waste. Examples of non-industrial waste include dry powder of sewage sludge, ashes from municipal refuge incinerators, and seashells. Also, examples of construction waste soil include soil and spoil produced from construction sites or demolishing sites, and discarded soil.

Depending on the compositions of the raw materials used for producing the burned product; in particular, in some cases where one or more materials selected from among the aforementioned industrial waste, non-industrial waste, and construction waste soil (hereinafter any of these wastes serving as a raw material will be collectively called “raw material waste”) are used as raw materials, C₄AF(4CaO.Al₂O₃.Fe₂O₃) may be formed. However, in the burned product of the present invention, a portion of C₂AS, preferably 70 or less wt. % of the weight of C₂AS may be replaced by C₄AF. Replacement by C₄AF beyond this range will narrow the temperature range for successful burning, thus making production control difficult.

The mineral composition of the burned product of the present invention can be calculated from the CaO content, SiO₂ content (wt. %), Al₂O₃ content (wt. %), and Fe₂O₃ content (wt. %) of the raw materials used, by the following equations. C₄AF=3.04×Fe₂O₃ C₃A=1.61×CaO−3.00×SiO₂−2.26×Fe₂O₃ C₂AS=−1.63×CaO+3.04×SiO₂+2.69×Al₂O₃+0.57×Fe₂O₃ C₂S=1.02×CaO+0.95×SiO₂−1.69×Al₂O₃−0.36×Fe₂O₃

Accordingly, when the raw material waste contains an insufficient amount of, for example, calcium, the shortage amount may be supplemented by the addition of limestone or a similar material. The proportion of the supplemental material is appropriately determined depending on the composition of the raw material waste, so that the composition of the resultant burned product falls within the scope of the present invention.

The burning temperature upon burning of the above raw materials is preferably 1,000 to 1,350° C., more preferably 1,200 to 1,330° C., for attaining an excellent melt phase during the burning step.

No particular limitations are imposed on the sintering apparatus. For example, a rotary kiln may be used. When burning is carried out by use of a rotary kiln, fuel substitute wastes, such as waste oils, scrap tire, and waste plastics may be used.

By such burning as described above, C₂AS is generated and the C₃A content becomes less than that obtained according to the Bogue's calculation, so that a burned product having the composition defined by the present invention can be obtained.

The cement admixture of the present invention is obtained by grinding the thus-obtained burned product. Gypsum may be added to a ground product of the burned product, in an amount of 1 to 6 parts by weight (on an SO₃ basis) with respect to 100 parts by weight.

No particular limitation is imposed on the grinding method. For example, a ball mill or a similar mill may be used in combination with a conventional grinding method. The resultant ground product of the burned product preferably has a Blaine specific surface area of 2,500 to 5,000 cm²/g, from the viewpoints of reduced bleeding, good fluidity, and ensured strength of mortar or concrete.

The cement of the present invention may be obtained by mixing 5 to 100 parts by weight of a ground product of the aforementioned burned product with 100 parts by weight of ground portland cement clinker. The mixing ratio between the two may differ depending on the type of cement. For example, when normal portland cement is of interest, the amount of the ground product to be mixed is preferably 5 to 50 parts by weight, more preferably 10 to 40 parts by weight, whereas when low-heat cement is of interest, the amount of the ground product to be mixed is preferably 50 to 100 parts by weight, more preferably 66 to 100 parts by weight.

The cement of the present invention may contain gypsum. When gypsum is incorporated, its amount (as calculated on a total SO₃ basis) is preferably 1.5 to 5 wt. %, more preferably 2 to 3.5 wt. %, most preferably 2.5 to 3 wt. %, of the cement, for ensuring typical coagulation properties. No particular limitations are imposed on the gypsum, and there may be used dihydrate gypsum, α- or β-hemihydrate gypsum, type-III anhydrous gypsum, or type-II anhydrous gypsum, among other gypsums, and these may be used singly or in aombination of two or more species.

The cement of the present invention may be produced by mixing the aforementioned components. No particular limitations are imposed on the method for mixing. For example, cement components including, e.g., portland cement clinker, the burned product, and gypsum, are mixed and then ground; or alternatively, respective components may be ground and then mixed together. Further alternatively, a cement admixture prepared by grinding the burned product and gypsum may be mixed with ground cement clinker, whereby a cement of the present invention can be obtained. The resultant cement preferably has a Blaine specific surface area of 2,500 to 4,500 cm²/g, from the viewpoints of reduced bleeding, good fluidity, and ensured strength of mortar or concrete.

EXAMPLES

The present invention will next be described in more detail by way of examples, which should not be construed as limiting the invention thereto.

Example 1

The burned products shown in Table 1 were prepared.

Briefly, the raw materials; i.e., limestone, ready-mixed concrete sludge, sewage sludge, and construction waste soil, were mixed at the proportions indicated in Table 1, and the resultant mixtures were burned in a small-scale rotary kiln at their corresponding temperatures shown in Table 1, so that a free lime content of 1% or less was attained. The chemical composition of each of the raw materials is shown in Table 2. TABLE 1 Raw materials employed Mineral composition (parts by weight) Burning (parts by weight) lime- Ready-mixed Sewage Waste temp. f- No. stone sludge sludge soil^(#)) (° C.) CaO C₂S C₂AS C₄AF C₃A 1 100 100 1270 0.6 100 51 37 0 2 100 90 1300 0.4 100 33 34 12 3 100 80 1320 0.5 100 15 30 26 4 100 1250 0.7 100 11 13 15 5 100 10 1250 0.7 100 29 5 17 6 100 50 1330 1.0 100 13 19 3 7 Industrial material 1450 0.9 100 5 0 5 8 Industrial material 1210 0.3 100 80 25 15 ^(#))Construction waste soil

TABLE 2 Ig. loss SiO₂ Al₂O₃ Fe₂O₃ CaO Na₂O P₂O₅ SO₃ MgO K₂O limestone 43.9 0.03 0.01 0.01 55.3 0.00 0.10 0.00 0.56 0.00 Ready- 0.0 24.88 7.60 2.96 56.69 2.76 2.02 0.21 0.56 0.00 mixed sludge Sewage 15.0 29.97 16.112 8.044 10.91 4.188 10.7 0.42 0.01 0.02 sludge Waste 13.3 52.7 13.8 8.7 2.5 1.5 0.5 2.7 1.2 1.94 soil^(#))

The burned product Nos. 7 and 8 were prepared by use of an industrial material. In the case of No. 7 product, in which C₂AS and C₄AF were contained only in a total amount of 5 parts by weight with respect to 100 parts by weight of C₂S, the free lime content became 1% or less at a burning temperature of 1,450° C. However, during cooling, dusting of the burned product occurred, permitting generation of γ-C₂S, which does not provide strength. On the other hand, in the case of No. 8 product, in which C₂AS and C₄AF were contained in a total amount of 105 parts by weight, granulation began to occur at 1,230° C., and a free lime content became 0.5% or less at 1,250° C. However, when the burning temperature is elevated further, the volume of liquefied matter extremely increased and melting occurred and thus, sintering could not be performed successfully.

Example 2

The clinkers used were normal portland cement clinkers having the compositions shown in Table 3. The gypsum employed was a dihydrate gypsum (product of Sumitomo Metal Industries, Ltd.). The clinker and gypsum were mixed with each of the burned products at the proportions shown in Table 4, followed by simultaneous grinding in a batch-type ball mill, so as to attain a Blaine specific surface area of 3,250±50 cm²/g, whereby a cement product was obtained.

Each of the thus-obtained cement products was evaluated in terms of heat of hydration, mortar flow, and mortar compressive strength. The results are shown in Table 4.

(Evaluation Method)

(1) Heat of Hydration:

Heat of hydration was measured according to JIS R 5203.

(2) Mortar Flow:

Mortar flow was measured according to JIS R 5201. Specifically, a mortar specimen was prepared by kneading for 5 minutes a mixture produced by incorporating a polycarboxylate-based air entraining and high water reducing agent in an amount of 0.8 wt. % with respect to the weight of cement (W/C=0.35 and S/C=2), and a flow cone specified in JIS R 5201-1997 was employed.

(3) Mortar Compressive Strength:

The mortar compressive strength values as measured on day 3, day 7, and day 28 were determined according to JIS R 5201. TABLE 3 Raw materials employed (parts by weight) Mineral composition Lime- Sewage Iron raw Silica Burning (parts by weight) stone sludge* material stone temp. (° C.) C₃S C₂S C₄AF C₃A OPC1 100 29 0.5 11 1500 100 25 16 14 OPC2 100 44 0 5 1450 100 19 24 20 *The composition is the same as that in Table 2

TABLE 4 Amount of Heat of Mortar flow burned hydration (mm) Mortar compressive Burned product (J/g) Immediately strength (N/mm²) No. Clinker SO₃*¹ product mixed*² 7d 28d after prep. 30 min. 3d 7d 28d 1 OPC1 2.0 — 0 335 388 185 155 29.1 44.2 62.5 2 OPC2 2.0 — 0 365 425 100 105 33.5 46.2 63.0 3 OPC1 2.0 No. 1 11 320 374 192 162 27.5 43.5 62.1 4 OPC1 2.0 No. 1 25 305 350 205 175 26.6 41.2 61.5 5 OPC1 2.0 No. 1 42 294 220 221 200 24.3 40.2 60.5 6 OPC2 2.0 No. 1 42 330 384 178 145 28.6 43.9 62.1 7 OPC1 2.0 No. 1 66 275 332 225 200 20.0 35.3 59.0 8 OPC1 2.0 No. 1 100 242 285 226 201 16.6 32.1 57.2 9 OPC1 2.0 No. 2 25 317 375 190 165 27.5 42.8 61.2 10 OPC1 2.0 No. 3 25 340 395 150 105 28.5 43.3 63.0 11 OPC1 2.0 No. 4 25 320 380 188 160 28.2 43.7 61.8 12 OPC1 2.0 No. 5 25 321 378 186 162 28.0 43.0 61.9 13 OPC1 2.0 No. 6 25 310 360 195 165 27.0 42.0 62.1 14 OPC1 2.0 No. 6 42 300 338 210 185 24.8 41.8 63.1 15 OPC2 2.0 No. 6 25 345 395 170 140 30.5 44.2 62.8 16 OPC1 2.0 No. 7 25 290 340 235 225 19.6 35.2 52.0 17 OPC1 2.0 No. 8 25 286 343 235 225 19.7 33.3 56.0 *¹wt. % with respect to cement *²Parts by weight with respect to 100 parts by weight of clinker

As is apparent from Table 4, as compared with OPC1 (No. 1), OPC2 (No. 2) exhibits a higher mortar compressive strength; however, heat of hydration is still high and mortar flow is significantly small. OPC2 incorporated a considerable amount of sewage sludge as a raw material, and therefore, the C₃A content and the C₄AF content became high, only to deteriorate fluidity. Accordingly, manufacture of normal cement clinker encounters difficulty when a relatively large amount of sewage sludge is used as a raw material. If use of sewage sludge as a raw material is desired, silica stone and iron raw material must also be incorporated as in the case of OPC1, resulting in a restricted amount of sewage sludge to be used. In contrast, the burned products of the present invention permit effective utilization of a relatively large amount of waste, such as swage sludge; and the burned products can be produced even from waste materials. Moreover, they can be added to conventional cement products without adversely affecting the strength or fluidity of the resultant mortar, concrete, or similar products.

A cement product produced by adding a burned product No. 1 to OPC1 exhibits a decrease in heat of hydration and an increase in mortar flow, as the added amount increases. However, as the added amount increased, strength at an initial material age (day 3, day 7) declined, and when the added amount was 42 parts by weight (No. 5), a relatively small compressive strength, in view of the normal cement standards, was obtained. When 42 parts by weight of a burned product was added to OPC2, the attained heat of hydration, mortar flow, and compressive strength were found to be comparable to those of OPC1.

Moreover, when the amount of a burned product added to OPC1 was 66 parts by weight or 100 parts by weight, the attained compressive strength was found to be relatively small in view of the standards for normal cement, with significantly reduced heat of hydration, and thus meeting the specifications for moderate heat cement or low-heat cement.

In the case where a burned product No. 2, having a high C₃A content as compared with a burned product No. 1, was used to thereby produce a cement product (No. 9), the heat of hydration was lowered as compared with that of OPC1, with an increased mortar flow. However, the effects attained by the burned product No. 2 were insignificant as compared with the burned product No. 1, though reduction in strength observed for the burned product No. 2 was smaller than that observed for the burned product No. 1.

In the case where a burned product No. 3, containing C₃A in an amount higher than 20 parts by weight with respect to 100 parts by weight of C₂S, was used to thereby produce a cement product (No. 10), although the compressive strength did not deteriorate, the heat of hydration increased as compared with that of OPC1, with a decreased mortar flow.

Without use of limestone, burned product Nos. 4 and 5 were produced by burning ready-mixed concrete sludge (and sewage sludge) alone. Each of these products was added to OPC1 by an amount of 25 parts by weight. The performance obtained was confirmed to be equivalent to that obtained from burned products produced by the employment of limestone.

In the case where each of burned product Nos. 7 and 8 was added to OPC1 by 25 parts by weight, heat of hydration was significantly reduced and mortar flow increased. However, compressive strength was drastically reduced, and did not recover even on day 28.

Example 3

(1) Production of Cement Admixture:

Each of the burned product Nos. 1 and 6 obtained from Example 1 was mixed with dihydrate gypsum (product of Sumitomo Metal Industries, Ltd.) at a ratio shown in Table 5, and ground in a batch-type ball mill so as to attain a Blaine specific surface area of 3,250±50 cm²/g, whereby an admixture was obtained.

(2) Production of Cement:

To cement No. 1 shown in Table 4 of Example 2, each admixture obtained as described above was mixed at different ratios shown in Table 5, to thereby produce cement products. The resultant cement products were evaluated in a manner similar to that described in Example 2, in terms of heat of hydration, mortar flow, and mortar compressive strength. The results are shown in Table 5. TABLE 5 Heat of Mortar flow Admixture hydration (mm) Mortar compressive Burned SO₃*¹ in mixing (J/g) Immediately strength (N/mm²) No. product admixture ratio*² 7d 28d after prep. 30 min. 3d 7d 28d 18 No. 1 2.0 11 315 370 193 160 28.0 43.8 64.5 19 No. 1 2.0 25 303 345 208 174 27.0 42.2 63.0 20 No. 1 2.0 42 290 315 222 197 25.0 42.6 62.3 21 No. 1 2.0 66 278 330 228 198 21.5 35.8 60.7 22 No. 1 2.0 100 245 290 228 198 17.0 32.5 59.1 23 No. 6 2.0 25 308 355 200 172 26.5 41.8 63.0 24 No. 6 2.0 42 295 332 218 191 24.2 41.5 63.5 *¹Parts by weight with respect to 100 parts by weight of a burned product *²Parts by weight with respect to 100 parts by weight of the cement linker

Test Example 1

Cement sample Nos. 1, 4, and 13 shown in Table 4 of Example 2, were used to produce concrete specimens, and the specimens were tested in terms of the slump, air volume, and compressive strength.

The compositions of the respective concrete specimens are shown in Table 6.

The slump, air volume, and compressive strength of each concrete specimen were measured in accordance with the methods specified in JIS A 1101, JIS A 1128, and JIS A 1108, respectively. The size of each specimen is +10×20 cm. The results are shown in Table 7. TABLE 6 Unit amount (kg/m³) Water Fine Coarse reducing Added AE Cement Water aggregate aggregate agent agent (%) 380 190 809 966 0.95 1.5 A Fine aggregate: Mixture (1:3 by mass) of sea sand and ground sand (F.M.: 2.93) Coarse aggregate: Ground stone 2005 (F.M.: 6.65) Water reducing agent: Pozzolith No. 70 (product of NMB) AE agent; 202 A (product of NMB)

TABLE 7 Compressive Added Slump (cm) Air volume (%) strength Burned burned Immediately Immediately (N/mm²) No. Clinker SO₃*¹ product product*² after prep. 30 min. 60 min. 90 min. after prep. 90 min. 3d 7d 28d 1 0PC1 2.0 — 0 17.3 12.6 10.7 8.2 4.1 3.0 22.5 33.5 42.8 4 0PC1 2.0 No. 1 25 20.5 14.5 13.5 12.5 5.0 3.5 20.1 32.0 41.5 13 0PC1 2.0 No. 6 25 19.3 13.2 12.5 10.8 4.7 3.2 20.9 32.8 42.5 *¹wt. % with respect to cement *²Parts by weight with respect to 100 parts by weight of clinker

Test Example 2

Cement specimens were prepared by adding the cement admixtures produced in Example 3 to cement No. 1 listed in Table 4 of Example 2. The amounts of addition are indicated in Table 8. Similar to Test Example 1, the slump, air volume, and compressive strength of the concrete specimens were measured. The results are shown in Table 8. TABLE 8 Compressive Added slump (cm) Air volume (%) strength Burned burned Immediately Immediately (N/mm²) No. product SO₃*¹ product*² after prep. 30 min. 60 min. 90 min. after prep. 90 min. 3d 7d 28d 19 No. 1 2.0 25 21.5 14.3 13.2 12.2 4.8 3.8 19.5 31.2 42.2 23 No. 6 2.0 25 20.5 14.0 12.8 11.5 4.5 3.2 20.0 31.8 42.2 *¹Parts by weight with respect to 100 parts by weight of burned product *²Parts by weight with respect to 100 parts by weight of cement clinker

Industrial Applicability

Through use of a cement admixture produced by grinding the burned product of the present invention, cement products exhibiting low heat of hydration and good fluidity can be obtained.

Moreover, the burned product of the present invention can be produced by making use of, as a raw material, industrial waste, non-industrial waste, or construction waste soil, and more advantageously can be produced exclusively from waste material, thereby enabling effective utilization of enormous volumes of waste. In addition, since the admixture of the invention can be produced through low-temperature burning of waste, fuel cost can be curtailed. 

1. A burned product containing 100 parts by weight of C₂S, 10 to 100 parts by weight of C₂AS, and 20 or less parts by weight of C₃A.
 2. The burned product according to claim 1, wherein a portion of C₂AS is replaced by C₄AF.
 3. The burned product according to claim 1 or 2, which is produced from a raw material of one or more species selected from among industrial waste, non-industrial waste, and construction waste soil.
 4. The burned product according to any one of claims 1 through 3, wherein burning is performed at 1,000 to 1,350° C.
 5. A cement admixture prepared by grinding a burned product as recited in any one of claims 1 through
 4. 6. A cement admixture containing 100 parts by weight of a ground product of a burned product as recited in any one of claims 1 through 4 and 1 to 6 parts by weight, as calculated on an SO₃ basis, of gypsum.
 7. A cement which contains 100 parts by weight of ground portland cement clinker and 5 to 100 parts by weight of a ground product of a burned product as recited in any one of claims 1 through
 4. 8. A cement according to claim 7, which contains gypsum in an amount of 1.5 to 5 wt. % as calculated on an SO₃ basis. 